Snap Shackles are generally discouraged as a means of attaching a jibsheet. Jib sheets tend to flog and catch on rigging parts. As a result snap shackles can really beat the living daylights out of the mast, are dangerous during foredeck work and can get hung up and come undone at less than perfectly desireable moments. Generally it is considered to be a better idea to tie the sheets on with a bowline.